Catalytic production of low pour point lubricating oils



United States Patent 3,486,993 CATALYTIC PRODUCTION OF LOW POUR POINTLUBRICATING OILS Clark J. Egan, Piedmont, and Robert J. White, Pinole,

Califl, assignors to Chevron Research Company, San Francisco, Calif., acorporation of Delaware No Drawing. Continuation-impart of applicationsSer. No.

477,597, Aug. 5, 1965, and Ser. No. 548,075, May 6,

1966. This application Jan. 24, 1968, Ser. No. 699,999

Int. Cl. C10g 23/00, 37/06, 13/00 US. Cl. 20889 6 Claims ABSTRACT OF THEDISCLOSURE In a process for reducing the pour point of heavy lubricatingoils without physically dewaxing the oils or diluting them withlow-boiling products, which comprises denitrifying and hydroisomerizingthe oils under specified conditions, it has been found that thehydroisomerization is made much more selective and the concurrenthydrocracking significantly reduced if the denitrified oil ishydrogenated to substantially eliminate the aromatic compounds prior tohydroisomerization. The hydroisomerized oil may be further hydrogenated,if desired, to improve the stability of the oil.

CROSS REFERENCES This application is a continuation-in-part of copendingapplication Ser. No. 477,597, filed Aug. 5, 1965 and now abandoned, andalso a continuation-in-part of copending application Ser. No. 548,075,filed May 6, 1966 and now abandoned.

BACKGROUND OF THE INVENTION This invention relates to processes forlowering the pour points of hydrocarbon oils and to processes involvingtreating lubricating oils with hydrogen in the presence of catalysts.

Hydrocarbon oils to be suitable for use as lubricants are generallyrequired to be sufficiently high boiling to have low volatility and ahigh flash point. Superior lubricating properties are obtained if theoil is composed primarily of saturated hydrocarbons comprising paraffinsand cycloparafiins, with a minimum content of aromatics. The oils arerequired to flow freely, and thus generally must have a pour point notin excess of about +35 F., and more usually pour points of +l F., +5 F.,or 0 F. or lower are specified. Many other oil products not designed foruse as lubricants, spray oils for example, desirably have these sameproperties of low volatility, high flash point, high paraffin content,and low pour point.

Normal parafiins and waxes present in virtually all highboiling portionsof crude petroleum impart a high pour point to the oil fractions asobtainable directly by distillation, and accordingly the oils must betreated to meet the low pour point specifications. Treating proceduresof two kinds have been described in the prior art. One type of procedureinvolves combining low-boiling materials (i.e., materials boiling belowabout 550 F.) with the highboiling portions or, if the initial oilcontains both highand low-boiling portions, leaving both portions in thefinished product. This procedure is unsatisfactory, for it produceswide-boiling range end products, which have components boiling below 550F. and are thus unsatis- "ice factory for use as lubricants. Anotherprocedure which is described in the art is one in which the high-boilingportions are dewaxed. The dewaxing procedures heretofore used have allrequired at least one step of physically separating wax from the oil,though a variety of procedures have been developed. Thus the oil may becooled to a low temperature suificient to crystallize out hard, normalparafiin wax; and the wax can then be physically separated byfiltration, centrifugation, or like methods. More commonly, solventdewaxing is employed wherein a solvent, such as a mixture ofmethylethylketone and benzene is added, which preferentially dissolvesthe nonwaxy hydrocarbons and lowers the oil viscosity withoutappreciably lowering the crystallization temperature of the wax, but thewax must still be separated physically as before. In addition, it isfrequently necessary to use mechanically complicated, internallyscraped, heat exchangers in the chilling procedures. Other methods havebeen devised involving forming complexes with the wax molecules, such asin the urea adduction process; but again a physical separation of thewax or wax adduct or complex is needed.

"The dewaxing methods heretofore used are quite costly to build and tooperate because of the large amount of equipment needed for themechanical handling, which must be done at low throughputs to accomplishthe physical wax separation. Thus in a typical process for producinglubricating oils comprising several steps-including, for example,solvent extraction, acid treating, hydrofining, clay contacting, andsolvent dewaxingthe dewaxing step is the most costly treating step.There have been some indications in the art that certain oils need onlypreferentially be dewaxed. However, examination of data disclosed inthis art makes clear that the oils in question are produced by processesin which only a few degrees reduction in pour point of the product oilsis achieved or in which the product oils contained some quantity oflowboiling materials; and the latter served to reduce the pour point ofthe product oils. It would, therefore, be highly desirable to be able tominimize or eliminate completely the need for dewaxing by physicalseparation of wax, which would require that some means be found forlowering the pour points of the available oils other than by dilution ofthe high-boiling oils with low-boiling materials.

SUMMARY As disclosed in our aforementioned copending applications, ithas been found that the pour points of heavy waxy oils can be loweredsufficiently to meet the low pour point specifications of lubricatingoils and similar products without recourse to any step involvingphysically separating wax. In accordance with the process disclosed insaid copending application Ser. No. 477,597, the pour point of a heavyoil is lowered by first substantially eliminating organic nitrogencompounds present in the oil and then contacting the nitrogen-free oilwith a reforming catalyst in a hydrocracking-hydroisomerization zone.The pour point lowering results from hydroisomerization of high pourpoint parafiins contained in the oil, and the conditions used in thehydroisomerization are such that the pour point lowering is accompaniedby hydrocracking. The hydrocracking lowers the yield of the desiredhigh-boiling oil products.

It has now been unexpectedly found that hydroisomerization of thenitrogen-free oil at temperatures in the DETAILED DESCRIPTION OF THEINVENTION To illustrate the nature of the improvements which can beaccomplished by means of the present invention, the following examplepresents a comparison of the results obtained by (1) the two-stageprocess of first subjecting a heavy waxy oil tohydrocracking-denitrification to sub stantially eliminate organicnitrogen compounds and then hydroisomerizing the high-boiling portion ofthe nitrogenfree oil, and by (2) the process of the invention wherein anaromatics hydrogenation step is interjected between the nitrogen removalstep and the hydroisornerization step.

'In addition, there are shown for comparison the results obtainable byconventional solvent dewaxing of the nitrogen-free oil.

EXAMPLE The residuum from vacuum distillation of mixed California crudeoils was subjected to propane deasphalting to obtain a metal-freeresidual oil in a yield of 57 percent, containing 7,400 p.p.m. organicnitrogen, 1.06 weight percent sulfur, and having a gravity of l6.1 API.The deasphalted oil is quite waxy, as a yield of only 88 percent oil isobtainable by solvent dewaxing to F. pour point. The undewaxedsolvent-deasphalted oil was contacted with a nickel sulfide-molybdenumsulfide-alumina-silica sulfactive hydrogenation catalyst at 800 F.,2,400 p.s.i.g., and 0.5-0.65 LHSV, in the presence of about 5,000 standard cubic feet of recycled hydrogen per barrel. The effluent oil wasfreed of H S and NH, and then distilled to recover a bottoms fractionboiling entirely above 750 F., obtained in a yield of 45 weight percentfrom the deasphalted oil. The hydrocracked oil boiling above 750 F.contained 2 p.p.m. nitrogen and 12 p.p.m. sulfur and had a pour point of105 F. This heavy nitrogen-free oil was separated into three portionswhich were separately treated as follows:

(A) A portion was subjected to conventional solvent dewaxing with amethylethylketone solvent to a pour point of 0 F., and the dewaxed oilwas then distilled into fractions with boiling ranges of 750-900 F.,representing a 140 neutral lubricating oil; 9001,000 F,. representing a400 neutral lubricating oil; and 1,000+ F. bottoms representing a brightstock.

(B) Another portion was contacted with a platinumon-alumina reformingcatalyst containing 0.4 weight percent platinum, 0.2 weight percentchloride, and 0.5 weight percent fluoride, at 800 F., 2,800 p.s.i.g.,0.4 LHSV, and about 10,000 standard cubic feet of recycled hydrogen perbarrel. The oil efiiuent of this contacting was distilled to obtaindistillate fractions and a bottoms fraction boiling entirely above 750R, which bottoms fraction was then further distilled into the fractionscorresponding to the 140 neutral, 400 neutral, and bright stock.

(C) The third portion of nitrogen-free heavy oil was contacted with ahydrogenation catalyst comprising 2 weight percent palladium on 87/13silica/alumina cracking catalyst support at a low temperature rangingbetween 250 F. and 300 F., at 2,300 p.s.i.g., 0.5 LHSV, with 6,300standard cubic feet of hydrogen per barrel. The hydrogenated oil wasthen contacted with the platinumalumina reforming catalyst in the samemanner as just described in (B) above, at a lower temperature of 756 F.

isomerized oil was then separated into the 140 neutral, 400 neutral, andbright stock fractions.

The following table summarizes the results obtained in the abovecomparisons, and shows the yields of the respective products which areobtainable from a given amount of solvent deasphalted oil feed by therespective techniques of the runs (A), (B), and (C) just described.

TABLE A B C Hydrocracking plus Hydrohydro- Hydro cracking genationcracking plus plus plus hydrohydrosolvent isomerisomer- Lube oilproducts from SDA oil feed dewaxing ization ization 140 Neutral:

Yield, bbls 2, 900 2, 700 2, 500 Viscosity, SUS at 210 F 42 41 41 V.I118 112 Pour point, F 0 +20 --5 400 Neutral:

Yield, bbls 1, 240 600 1, 100 Viscosity, SUS at; 210 F 60 57 57 V.I 108118 I201g paint, F 0 +30 30 Bri i: toc

Yield, bbls 1, 100 350 400 Viscosity, SUS at 210 F 97 90 102 VI 115 114115 Pour point, F 0 +20 Micro solid pt, F. -56

As shown, the largest yield of the respective lubricating oil fractionsis obtained by solvent dewaxing the hydrocracked nitrogen-free oil. Butbesides being the most expensive technique, this system also has thedisadvantage that the viscosity index of the neutral, and of the 400neutral, is lower than obtained in the other runs. If the solventdewaxing is carried further so as to obtain a lower pour point thanshown, the viscosity index is even lower. Particularly to be noted isthat the hydrocracking+ hydroisomerization process of column B issubstantially improved by the interjected hydrogenation step, as shownin column C. In particular, a higher yield of 400 neutral distillate anda higher yield of bright stock are obtained, with only slightly loweryield of 140 neutral; and the pour points of all the respectivefractions are much lower than obtained by the isomerization without theprehydrogenation.

Further, the improved process shown in column C permits operation of thehydroisomerization step at a temperature more than 45 F. lower than thatrequired by the process of column B. This results in longer catalystlife, lower fouling rates, and lower costs for construction andmaintenance of equipment. Thus the prehydrogenation unexpectedly causeda marked increase in the selectivity of the hydroisomerization step suchthat a greater reduction in pour point could be obtained at the same ora lower temperature with less hydrocracking. It had already beenestablished that, without the prehydrogenation, higher temperatures ofhydroisomerization causing even more hydrocracking would have to be usedto obtain the low pour points.

In the hydrogenation with the palladium on silicaalumina catalyst, theconcentration of aromatics in the nitrogen-free oil was lowered fromabout 11 weight percent to less than 1 weight percent. Specifically, theaniline point of the nitrogen-free oil boiling above 750 F. recoveredfrom the first hydrocracking-denitrification was 246 F.; and the anilinepoint of the hydrogenated oil fed to the hydroisomerization with theplatinum-alumina catalyst was 263 F. The hydrocracking-denitrificationstep itself can be effective in lowering the aromatics content of theheavy oil feed to less than about 5 percent, if the temperature used isnot too high; but it is not possible thereby to obtain the very lowaromatics concentrations contemplated in the practice of this invention.It is considered that for best results the aromatics concentrationshould be lowered to below 1 weight percent, which requires the use of alower temperature than used in the denitrification and the use of anactive hydrogenation catalyst.

The catalyst used in the hydrogenation step of the present inventioncomprises an active hydrogenating metal component associated with asolid inorganic oxide carrier. The hydrogenating metal component ispreferably a noble metal of the platinum-palladium group, but nickel mayalso be used if higher concentrations of the metal are provided in thecatalyst. Usually the catalyst will contain from 0.1 to weight percentnoble metal, with amounts in the range 0.33 weight percent beingpreferred in view of the cost of these metals. The balance of thecatalyst, as mentioned, is a refractory inorganic oxide carrier lendinghigh porosity and surface area to the composite. Carriers having porediameters of about 100 Angstroms or more are preferred. Alumina is aneminently suitable carrier, but mixed oxides, such as silica-alumina,can also be employed; and these can be of the acidic, high silicacontent, type used as cracking catalysts or of the lower silica contenttype, having only moderate or low acidity and cracking activity.

The catalysts can be prepared by conventional impregnation,coprecipitation, or coagulation techniques. They are invariablysensitive to nitrogen compounds and also, to a lesser extent, to sulfurcompounds. Accordingly, the hydrogenation step is to be applied to theoil only after any organic nitrogen compounds present have beensubstantially removed. Preferably the nitrogen content does not exceed10 p.p.m., and the sulfur content does not exceed 50 p.p.m. Morepreferably, the nitrogen content is less than 1 p.p.m., and the sulfurcontent will be correspondingly lower. The catalyst employed in theabove-described example for the hydrogenation step-i.e., the palladiumon silica-alumina catalystis more resistant to deactivation by sulfurcompounds than most platimum catalysts, and can accordingly be used togreat advantage.

Conditions used in the hydrogenation step for substantially eliminatingaromatics includes temperatures of 200650 F. and pressures of1,000-5,000 p.s.i.g., preferably at least 1,500 p.s.i.g. Lowtemperatures, preferably 250450 F., are used with catalysts comprisingacidic carriers whereas temperatures of 500600 F. are preferred if thecatalyst has only low or moderate acidity, low enough to preventhydrocracking occurring to any substantial extent. At the high pressureand low temperature, with adequate contact time the aromatic compoundspresent can be essentially completely saturated with practically nosplitting or hydrocracking even if the catalyst used is of a type whichwould have substantial hydrocracking activity at higher temperatures of700 F. or above for example. The space velocity used will be in therange of 0.2-10 LHSV, preferably 0.3-3 LHSV, depending on theconcentration of aromatics in the nitrogenfree oil; and the throughputof hydrogen-rich gas, which may be recycled, should be at least 1,000s.c.f./bbl. with larger amounts in the range 2,00020,000 s.c.f./bbl.being preferred even though hydrogen consumption may be less than 500s.c.f./bbl. v

The hydrogenation catalyst could in some cases be provided as a separatebed in the inlet portion of a single reactor, the lower or downstreamportion of which contains the isomerization catalyst. The necessity tooperate at greatly different temperatures in the respective reactionzones, however, frequently makes it more desirable to use separatereaction vessels, which is also more advantageous where large quantitiesof oil are to be treated. Also the hydrogenation catalyst may tend tolose activity more rapidly than the isomerization catalyst becauseexposed to the nitrogen compounds still remaining in the oil andprotecting the isomerization catalyst from them. Thus it may be desiredto regenerate or replace the hydrogenation catalyst more often than theothers.

Feedstocks which may be successfully treated in accordance with theinvention include high pour point heavy oils, which must boil at leastpartly above 700 F. More desirably, the oil feed boils mostly above 800F. and at least partly above 900 F. A preferred feed is at least asheavy as a straight-run vacuum gas oil, and the most preferred feed is adeasphalted residual oil. The residual oil is required to benonasphaltic because the asphaltenes, being polynuclear aromatic-typecompounds, interfere with the conversion of paratfins in the process ofthe invention and also tend to rapidly reactivate the catalysts used.The deasphalting treatment applied in preparing the preferred feed maybe the type of deasphalting used in preparing heavy catalytic crackerfeedstocks; i.e., treatment with a light hydrocarbon solvent, such apropane, butane, pentane, or mixtures thereof, at near the criticalpoint of the solvent. The treatment may be such as to recover as feedthe entire so-called 'maltene fraction, comprising oil and resins,rejecting only the asphaltenes. The deasphalted oil feeds treated inaccordance with the invention will have high pour points of above +35 F,and more usually of at least +50 F. Thus a deasphalted oil feed willcontain sufficient high melting paraffins such that at least about 10weight percent of the feed would have to be separated as wax to obtain apour point of 0 F. by prior art solvent dewaxing methods.

As the first stage of the process, nitrogen compounds in the oil aresubstantially eliminated. This is best done by hydrogenation, whereinthe impure high pour point oil feed and hydrogen are passed at elevatedpressure above 1,000 p.s.i.g. through a reaction zone to contact thereina sulfactive hydrogenation catalyst having hydrocracking and.denitrification activity until organic nitrogen and sulfur compoundsinherently present in the raw feed are substantially eliminated. At theconditions required to accomplish the substantially complete conversionof organic nitrogen to ammonia, substantial hydrocracking of the oil tolower boiling distillates occurs. While it would appear desirable tominimize such hydrocracking conversion so as to maximize the yield ofhigh-boiling product, it appears that at least about 20 percentconversion of the feed to distillates lower boiling than the feed isneeded to obtain a high overall pour point reduction and to improve theviscosity index of the product. With residual oil feeds the mostpreferred conversion range appears to be from about 30 percent to about60 percent to distillates boiling below 700 F. The conversion isaccompanied by the consumption of substantial amounts of hydrogen,amounting usually to about 500 standard cubic feet or more per barrel ofoil.

Conditions used in the first stage hydrocracking-denitrification includetemperatures of 650900 F., more desirably 700850 F. The pressure shouldbe at least about 1,000 p.s.i.g. and may range upwards of 5,000p.s.i.g., with the preferred range being 1,500-4,000 p.s.i.g. Thethroughput of hydrogen-rich gas, which may be recycled, should be atleast 1,000 s.c.f./bbl. of feed, more usually 2,000-20,000 s.c.f./bbl.,with the preferred range being 4,000l0,000 s.c.f./bbl. The contact timebetween oil and catalyst is sufficiently long to accomplish the desirednitrogen removal and hydrocracking, which can generally be accomplishedat space velocities of 02-10 volumes of oil per hour per volume ofcatalyst (LHSV), preferably 0.3-3 LHSV.

The catalyst used in the first step may be of the sulfactivehydrogenation type commonly used for desulfuri zation anddenitrification. Suitable catalysts include combinations of the Group VIand Group VIII metals, oxides, or sulfides, associated with porousrefractory oxide carriers. Most suitable metals are nickel or cobalt incombination with molybdenum or tungsten as sulfides. The refractoryoxide may be alumina, or combinations of alumina with silica, magnesia,zirconia, titania, and like materials, or combination of such otheroxides, for example silica-magnesia. Such catalysts can be prepared in avariety of ways, including preparing the porous carrier first and thenimpregnating it with solutions of the metal compounds which are laterconverted to metal oxides by calcining. Particularly good catalysts foruse in the first stage hydrocracking can be prepared by coprecipitationtechniques wherein all of the components are initially supplied asdissolved compounds in aqueous solutions and coprecipitated together.

The conditions in the first stage hydrocracking should be such as tosubstantially eliminate organic sulfur compounds by conversion to H 5 inaddition to substantially eliminating organic nitrogen compounds byconversion to NH Usually the nitrogen conversion is the more difficultto accomplish, and accordingly if the organic nitrogen content has beenreduced to satisfactory levels, the organic sulfur concentration willalso have been sufiiciently reduced. In some rare cases, however, aswhere the impure oil feed has an unusually high sulfur content andunusually low nitrogen content, it may be possible to achieve asatisfactorily low nitrogen concentration without having removedsufficient sulfur. In those cases the contacting should be continueduntil the sulfur concentration has been lowered to below about 50 ppm.

Some pour point reduction may occur during the hydrocracking with thedenitrification catalyst, but not sufficient to lower the pour point ofthe highest boiling portion of the oil feed from above l35 F. to below+15 F. unless the conversion is continued far beyond what is needed inaccordance with the present invention, thereby greatly reducing productyield. There is evidence that, in the first stage hydrocracking, normalparaffins are cracked and isomerized to moderately branched isoparafiinswhich, however, still impart a high pour point to the oil. Theseisoparafiins are removable by solvent dewaxing techniques, and theywould have to be so removed in accordance with prior art techniques toobtain an acceptable low pour point product from the oil efiiuent of thefirst stage hydrocracking.

In accordance with the invention, the hydrocracked oil efiiuent of thefirst stage is not dewaxed; but instead at least a high-boiling portionof the oil effiuent and hydrogen is passed at elevated pressure above1,000 p.s.i.g. through the hydrogenation zone and then through a pourpoint reducing reaction zone, which may also be referred to as ahydroisomerization zone or a hydrocrackinghydroisomerization zone. Theoil effluent of the pour point reducing reaction zone is distilleddirectly into fractions including a highest boiling portion having a lowpour point which is at least 30 F. lower than the pour point of the highpour point purified oil effluent of the hydrocracking-denitrificationreaction zone.

Conditions used in the pour point reducing reaction zone includetemperatures of 750900 F., preferably 750850 F.; pressures of 500-5,000p.s.i.g.; more usually 1,0003,000 p.s.i.g.; hydrogen-rich gas throughputrates greater than 1,000 s.c.f./bbl. of oil, generally 2,000- 20,000s.c.f./bbl., and preferably 4,000l0,000 s.c.f./bbl. The contact time interms of liquid hourly space velocity is from 0.2l0, preferably 0.3-3LHSV. Variation of any of the reaction conditions outside these rangesmeans that some or all of the other process variable must be set at orbeyond their stated limits. Thus, for instance, if a lower temperaturethan 750 F. is used, an LHSV which is unreasonably high from anoperational standpoint must be maintained. Further, operation outsidethe stated ranges produces products with high pour points and/or otherundesirable characteristics which make them unsuitable as lubricants.The required conditions are such that at least weight percent of the oilentering this final reaction zone is hydrocracked to lower boilingdistillates, and usually at least about 20 percent hydrocrackingconversion is accomplished. The higher the percent conversion to lowerboiling distillates, the greater the pour point reduction that isachieved.

When the oil is prehydrogenated in accordance with the present inventionprior to hydroisomerization, the desired pour point reduction isachieved with substantially less conversion to lower boiling distillatesthan is the case without prehydrogenation. Nevertheless, with residualoils it still appears desirable that the conversion be at least about 30weight percent, especially if the pour point of the nitrogen-free oilrecovered from the first stage is above about F.

The catalyst employed in the pour point reducing hydroisomerization zoneis described as a naphtha reforming catalyst having no more thanmoderate acidity. A catalyst which has only moderate acidity is hereindefined to mean one that is less acidic than a catalyst supported onalumina containing more than two weight percent halide or a catalystsupported on a silica-alumina support which contains more silica thanalumina. Such a catalyst typically comprises a Group VI metal oxide or aGroup VIII metal hydrogenation-dehydrogenation component, desirably anoble metal, preferably platinum or palladium, associated with a porousrefractory oxide carrier, such as alumina, and which may be inherentlymoderately acidic or moderately acidified with no more than about twoweight percent of halide. The reforming catalyst is an activeisomerization catalyst. Nitrogen and sulfur compounds may deactivatesuch a catalyst, and accordingly these heteroorganic compounds aresubstantially excluded from the oil. Thus a typical preferred catalystcomprises essentially alumina promoter with a small amount, 0.1-2percent of platinum metal and a small amount, less than 1 percent, ofchloride and/or fluoride. This is a well-known platinum reformingcatalyst, but its action is quite different at the conditions used inthe pour point reducing zone. There is a net consumption of hydrogen,and instead of forming aromatics from naphthenes, the essential reactionoccurring appears to be one of hydrocracking and isomerizing moderatelybranched isoparafi'ins to highly branched isoparafiins. Instead of purealumina or halided alumina as the carrier or support, there may be useda moderately acidic alumina-silica cogel or coprecipitate containingmore alumina than silica. For example, good results have been obtainedusing a 2 percent palladium catalyst on 82 percent alumina-l8 percentsilica. Other analogous carriers and supports suitable for use willsuggest themselevs to those skilled in the art. The silica-aluminamaterials containing more silica than alumina, such as crackingcatalysts, do not appear to be good supports for the catalysts becausethey are too strongly acidic and adversely affect selectivity for theisomerization of isoparaffins.

We have obtained best results in the hydroisomerization step per seusing a platinum-alumina reforming catalyst containing only a smallamount of halides, from 0 to 1 weight percent total. The known noblemetal isomerization catalysts containing upwards of 2 weight percenthalide appear to be too acidic and have low selectivity at theconditions employed in the process of this invention, accomplishing lessisomerization and more hydrocracking and tending to become deactivtedmore rapidly. It is known from the art that, as halogen level increases,the yield of lubricating oil product of a given pour point decreases.Conversely, in order to obtain a large pour point reduction with a highhalide content catalyst, a substantial loss of product oil yield must betaken. For instance, the reduction in pour point achieved by a catalystcontaining 0.4 weight percent platinum and 0.7 weight percent halide isapproximately twice that achieved at the same yield of a '800-l,000 F.lubricating oil by a catalyst containing the same amount of platinum but3.9 weight percent halide. At higher halide levels, the superiority ofthe low halide catalyst would be even more marked. Further, the lowhalide catalyst as used in the present process has been shown to have anorder of magnitude greater pour point reducing ability than the samecatalyst as used in prior art processes. Thus in one comparison, in aprior art process the catalyst containing 0.7 weight percent halideproduced a F. pour point reduction; while in the process of thisinvention a similar catalyst produced a 55 F. pour point reduction. Thehydrogenation step of this invention is accordingly used to greatestadvantage in conjunction with a process wherein there is employedhydroisomerization catalysts of no more than moderate acidity.

It will be recognized that the contacting of the oil and hydrogen withthe catalyst in the respective reaction zones may be carried out in avariety of well-known ways including the use of fixed beds of catalystparticles in high pressure reactors through which the hydrogen and oilflow concurrently or countercurrently. This appears to be the mostpractical and convenient method, but other known techniques can be usedsuch as those involving the use of fluidized circulating catalystparticles, catalyst slurries, and gravitating catalyst masses.

The metal hydrogenation-dehydrogenation components of the catalystsemployed in the hydrogenation and hydroisomerization stages should beused and maintained in the non-sulfided state. Noble metals of theplatinum group are preferred in both of these latter stages becausetheir sulfides are unstable, and the catalysts can accordingly toleratea small amount of sulfur in the feed without becoming irreversiblysulfided. For example, the palladium catalyst used in the hydrogenationstep of the example herein declined in activity during use whiletreating the 12 ppm. sulfur oil. Most of the lost activity could beregained by flowing H over the catalyst for a few hours at temperaturesabove 750 F. Nickel is less advantageous in these catalysts because itforms a stable sulfide, and its use would require that sulfur compoundsbe virtually completely excluded. In the denitrification stage, whereinsulfided catalysts are used to greatest advantage, highly branchedisoparafiins are not readily formed so that an excessively highhydrocracking con-. version would be needed to obtain a substantiallowering of the pour point. By nuclear magnetic resonance it has beenshown that the ratio of CH groups to CH groups is about 30 percentgreater in a low pour point oil product of the hydroisomerization stagethan in a low pour point (solvent dewaxed) sample of the correspondingoil product of the hydrocracking-denitrification stage. The higher ratioshows that the isoparaffins are more highly branched. Thus furtherbranching of both high pour point and low pour point isoparafiins isaccomplished in the isomerization stage, which could not be accomplishedin the first stage with the sulfided catalyst.

The low aromatics content of the hydrogenated oil passed to thehydroisomerization zone in the practice of this invention is usuallyreflected in a very low aromatics concentration in the final oilpro-ducts. In some cases this can be undesirable as many of theadditives conventionally put into lubricating oil products as ultimatelysold depend on the oil having some aromatics to aid in dissolving thesaid additives. In such cases, a small amount of aromatics can be addedto the hydroisomerized oil, as the purpose of removing the aromatics byhydrogenation was to improve the selectivity in the hydroisomerizationstep; and it is not essential to most lubricating oils that they beabsolutely free of aromatics.

In some instances, possibly because of the presence of small amounts ofcondensed aromatic species, the oils produced by the process of thisinvention may exhibit some instability to oxidation in the presence oflight. This can be corrected by known low cost treatments includingtreating with sulfuric acid or clay contacting. A finishinghydrogenating, at low temperature conditions and with a catalyst such asused in the intervening hydrogenation, has been found particularlyeffective in stabilizing the low pour point oils produced by the methodof this invention. Thus in some cases a four-stage hydrogen treatingprocess is contemplated comprising: first, a denitrification attemperatures above about 700 F. using a sulfactive catalyst; second, ahydrogenation at temperatures below about 650 F. using anitrogen-sensitive catalyst; third, a hydroisomerization at temperaturesabove about 750 F. using a reforming catalyst; and fourth, ahydrogenation at temperatures below about 650 F. using any suitablehydrogenation catalyst; all at elevated hydrogen partial pressure.Catalysts and conditions used in the final hydrogenation are preferablylike those previously described herein as usable in theprehydrogenation.

For example, a solvent deasphalted oil was denitrified by contact with anickel-tungsten sulfide catalyst at 0.4 LHSV, 785 F., 2,400 p.s.i.g. and5,000 s.c.f./bbl. hydrogen. The 750 F.+ product was hydrogenated bycontact with a 2 percent palladium on acidic silica-alumina catalyst at0.2 LHSV, 350 F., 3,000 p.s.i.g. and 6,400 s.c.f./bbl. hydrogen. Thehydrogenated product was hydroisomerized and then hydrogenated forstabilization by contact first with a 0.4 percent platinum on aluminacatalyst at 0.4 LHSV, 754 F., 2,600 p.s.i.g. and 5,000 s.c.f./bbl.hydrogen and then with a 2 percent palladium on silica-alumina catalyst,containing less silica than the similar catalyst used in theprehydrogenation, in the lower part of the same reactor at 0.8 LHSV, 500F., 2,600 p.s.i.g. and 5,000 s.c.f./bbl. hydrogens. The 750 F.i+oil fromthe above process is stable to air and sunlight for longer than 20 days.Comparable samples of oils not subjected to the final hydrogenation withthe palladium catalyst show evidence of instability in less than 3 days.

It is apparent that many diiferent embodiments of this invention may bemade without departing from the scope and spirit thereof, and thereforeit is not intended to be limited except as indicated in the appendedclaims.

We claim:

1. A process for reducing the pour point of a heavy oil containingaromatics and organic nitrogen compounds without physically dewaxingsaid oil or diluting said oil with low boiling materials, comprisingfirst substantially eliminating organic nitrogen compounds present insaid heavy oil and simultaneously converting at least 20 percent of saidheavy oil to distillates lower boiling than said heavy oil, and thensubstantially eliminating aromatics in the essentially nitrogen-free oilby contacting said essentially nitrogen-free oil with an activehydrogenation catalyst in the presence of hydrogen at a temperature inthe range of 200650 F., and a pressure in the range of 1,0005,000p.s.i.g., followed by simultaneous hydrocracking and hydroisomerizationof the essentially nitrogenand aromatics-free oil over a naphthareforming catalyst comprising a noble metal associated with alumina andcontaining no more than two weight percent halide in the presence ofhydrogen at a temperature of 750-900 F. and a pressure of 1,0005,000p.s.i.g., whereby said elimination of aromatics makes saidhydroisomerization more selective for lowering the pour point of saidessentially nitrogenand aromatics-free oil with less simultaneoushydrocracking, permitting recovery of a product oil with a pour point atleast 30 F. lower than the pour point of said essentially nitrogen-freeoil.

2. The process of claim 1 wherein said hydrogenation catalyst comprisesa noble metal associated with a porous carrier.

3. The process of claim 1 wherein said naphtha reforming catalystcomprises a noble metal associated with a porous alumina carriercontaining 01 weight percent halide.

4. The process of claim 1 wherein said substantial elimination oforganic nitrogen compounds reduces the nitrogen content of the oil toless than 10 ppm.

5. The process of claim 1 wherein the aromatics content of saidessentially nitrogen-free oil is reduced to less than 1 percent.

6. The process of claim 1 further characterized in that said product oilis subjected to a finishing hydrogenation catalyst comprising contactingsaid product oil with a hydrogenation catalyst at an elevated pressureand a temperature below about 62 0" F. in the presence of 3,132,0865/1964 Kel ie? et a1. 20857 hydrogen, and recovering a lubricating oilof improved 3,268,439 8/1966 Tnpman et a1 2O8112 Stability ReferencesCited DELBERT E. GANTZ, Primary Examiner UNITED STATES PATENTS 5 T. H.YOUNG, Assistant Examiner 2,967,147 1/1961 Cole 208144 U.S. C1. X.R.

3,125,511 3/1964 Tupman et a1 208264 20858

